1. Suppose you put more than one kind of ammunition (say, alchemical cartridge) in the same pouch. Is there any penalty to your action economy to draw a particular type, or could a gunslinger with the usual feats and abilities still reload correctly as a free action?
2. Some clothing or gear contain multiple pockets, such as a backpack or adventurer's sash. Does the sash count as one container for the purpose of spells targeting containers (such as abundant ammunition) or does each pocket count as the container?
3. The endless bandolier and beneficial bandolier have loops to hold individual cartridges. Do these count as individual containers or does the entire bandolier count as a container (or neither)?
Okay, I'll bite.
1. I'd say no, but wouldn't enforce it. Haversacks place what you want at the top and that's a move action. However, if you enforced this sort of thing for everyone else, by all means enforce it for your gunslinger.
2. Depends on what you are specifically trying to do. I'd say targeting a pocket destroys the pocket, but destroying a coat would make unwearable. Backpack are just big pockets with a strap so both.
3. Same, with the added suck of having a magic item destroyed.
I should clarify: The spells in question do not damage or destroy the container. They are spells that enhance the container or the items inside, and they specifically work on containers.
School conjuration (summoning); Level bard 1, cleric 1, ranger 1, sorcerer/wizard 1
Casting Time 1 standard action
Components V, S, M/DF (a single piece of ammunition)
Target one container touched
Duration 1 minute/level
Saving Throw none; Spell Resistance no
When cast on a container such as a quiver or a pouch that contains nonmagical ammunition or shuriken (including masterwork ammunition or shuriken), at the start of each round this spell replaces any ammunition taken from the container the round before. The ammunition taken from the container the round before vanishes. If, after casting this spell, you cast a spell that enhances projectiles, such as align weapon or greater magic weapon, on the same container, all projectiles this spell conjures are affected by that spell.
There are other spells; greater magic weapon doesn't target a container but specifies that one or more ammunition must be in the same container. It isn't clear whether an object with multiple pockets such as a backpack, adventurer's sash, handy haversack, or one of the magic bandoliers is considered one container or multiple containers.
I'm not as familiar with gunslingers as I'd like to be, but I can't imagine that he'd have any more difficulty retrieving the desired ammo than an archer does if she mixes various arrows.
I don't believe the intent is to be pedantic about "what is a container?".
Most containers have at least a few pockets, and I would expect the spell to affect them all.
In the case of some of the items (like the haversack) that specifically call out various discrete dimensional spaces, I don't think it's unreasonable to name them as different containers... but I'm also not 100% convinced that's the intent in regard to the spell.
Certainly the entire strip containing bullets on the bandoliers should count as a contiguous space, but does that extend to everything?
I guess the yardstick I'd use is along the lines of, "if your interpretation of a (positive) spell needlessly complicates what should be simple/straightforward, you're doing it wrong"
(but in terms of pointing out where RAW might be lacking: nice)